I generally tune my 7th string to low A, so I've found that the D'Addario .058 and .060 give me a great, full sound without being too loose to really hit.
Lester Devoe Flamenco Negra
Lester Devoe Flamenco Blanca
Aparicio Flamenco Blanca with RMC pickup
Bartolex 7-string with RMC pickup
Giannini 7-string with Shadow pickup
Sal Pace 7-string archtop